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Learn more about two great innovative camera features

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Fast and precise, flat and wide

Front side or back side illuminated sensors

Conventional sensors are designed to convert the light falling on the
front side of the sensor to electrons. As discussed in the article Pixel size and well capacity not all
the sensor surface is sensitive to light as the pixel also needs control
electronics limiting the fill factor.

As we see higher resolution sensors
come to market utilising the same sensor size, we see pixel sizes reduce
in some cases to under 2 microns. This reduction has the effect of
reducing this fill factor further as the area for the control electronics
becomes more significant.

To maximise sensitivity we are seeing
additional optical lightguides added to microlenses to channel as much
light as possible to the limited photosensitive area, however a new
approach is now being seen in some of the latest small pixel sensors
that overturn the pixel design to illuminate the pixel from the back side
(Back side illuminated or BSI), so the control electronics do not limit the
light sensitive area. Due to the structure of the silicon pixel, light in a BSI
sensor has to travel further into the silicon to be converted into
electrons and is therefore less efficient at converting the light (lower
quantum efficiency or QE).

We therefore see a tipping point of pixel
sizes between 1 and 2 μm where a BSI sensor will deliver more signal
than a traditional front side illuminated (FSI) pixel. As we see the sensor
resolution continue to increase, we will see more sensors using this
technique.